selftests/bpf: fix uprobe offset calculation in selftests

Fix how selftests determine relative offset of a function that is
uprobed. Previously, there was an assumption that uprobed function is
always in the first executable region, which is not always the case
(libbpf CI hits this case now). So get_base_addr() approach in isolation
doesn't work anymore. So teach get_uprobe_offset() to determine correct
memory mapping and calculate uprobe offset correctly.

While at it, I merged together two implementations of
get_uprobe_offset() helper, moving powerpc64-specific logic inside (had
to add extra {} block to avoid unused variable error for insn).

Also ensured that uprobed functions are never inlined, but are still
static (and thus local to each selftest), by using a no-op asm volatile
block internally. I didn't want to keep them global __weak, because some
tests use uprobe's ref counter offset (to test USDT-like logic) which is
not compatible with non-refcounted uprobe. So it's nicer to have each
test uprobe target local to the file and guaranteed to not be inlined or
skipped by the compiler (which can happen with static functions,
especially if compiling selftests with -O2).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220126193058.3390292-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 29 insertions, 21 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
index d0bd51eb23c8..d48f6e533e1e 100644
--- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
+++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
@@ -5,9 +5,10 @@
 /* this is how USDT semaphore is actually defined, except volatile modifier */
 volatile unsigned short uprobe_ref_ctr __attribute__((unused)) __attribute((section(".probes")));
 
-/* attach point */
-static void method(void) {
-	return ;
+/* uprobe attach point */
+static void trigger_func(void)
+{
+	asm volatile ("");
 }
 
 void test_attach_probe(void)
@@ -17,8 +18,7 @@ void test_attach_probe(void)
 	struct bpf_link *kprobe_link, *kretprobe_link;
 	struct bpf_link *uprobe_link, *uretprobe_link;
 	struct test_attach_probe* skel;
-	size_t uprobe_offset;
-	ssize_t base_addr, ref_ctr_offset;
+	ssize_t uprobe_offset, ref_ctr_offset;
 	bool legacy;
 
 	/* Check if new-style kprobe/uprobe API is supported.
@@ -34,11 +34,9 @@ void test_attach_probe(void)
 	 */
 	legacy = access("/sys/bus/event_source/devices/kprobe/type", F_OK) != 0;
 
-	base_addr = get_base_addr();
-	if (CHECK(base_addr < 0, "get_base_addr",
-		  "failed to find base addr: %zd", base_addr))
+	uprobe_offset = get_uprobe_offset(&trigger_func);
+	if (!ASSERT_GE(uprobe_offset, 0, "uprobe_offset"))
 		return;
-	uprobe_offset = get_uprobe_offset(&method, base_addr);
 
 	ref_ctr_offset = get_rel_offset((uintptr_t)&uprobe_ref_ctr);
 	if (!ASSERT_GE(ref_ctr_offset, 0, "ref_ctr_offset"))
@@ -103,7 +101,7 @@ void test_attach_probe(void)
 		goto cleanup;
 
 	/* trigger & validate uprobe & uretprobe */
-	method();
+	trigger_func();
 
 	if (CHECK(skel->bss->uprobe_res != 3, "check_uprobe_res",
 		  "wrong uprobe res: %d\n", skel->bss->uprobe_res))
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
index 5eea3c3a40fe..cd10df6cd0fc 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
@@ -8,6 +8,12 @@
 #include <test_progs.h>
 #include "test_bpf_cookie.skel.h"
 
+/* uprobe attach point */
+static void trigger_func(void)
+{
+	asm volatile ("");
+}
+
 static void kprobe_subtest(struct test_bpf_cookie *skel)
 {
 	DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
@@ -62,11 +68,11 @@ static void uprobe_subtest(struct test_bpf_cookie *skel)
 	DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
 	struct bpf_link *link1 = NULL, *link2 = NULL;
 	struct bpf_link *retlink1 = NULL, *retlink2 = NULL;
-	size_t uprobe_offset;
-	ssize_t base_addr;
+	ssize_t uprobe_offset;
 
-	base_addr = get_base_addr();
-	uprobe_offset = get_uprobe_offset(&get_base_addr, base_addr);
+	uprobe_offset = get_uprobe_offset(&trigger_func);
+	if (!ASSERT_GE(uprobe_offset, 0, "uprobe_offset"))
+		goto cleanup;
 
 	/* attach two uprobes */
 	opts.bpf_cookie = 0x100;
@@ -99,7 +105,7 @@ static void uprobe_subtest(struct test_bpf_cookie *skel)
 		goto cleanup;
 
 	/* trigger uprobe && uretprobe */
-	get_base_addr();
+	trigger_func();
 
 	ASSERT_EQ(skel->bss->uprobe_res, 0x100 | 0x200, "uprobe_res");
 	ASSERT_EQ(skel->bss->uretprobe_res, 0x1000 | 0x2000, "uretprobe_res");
diff --git a/tools/testing/selftests/bpf/prog_tests/task_pt_regs.c b/tools/testing/selftests/bpf/prog_tests/task_pt_regs.c
index 37c20b5ffa70..61935e7e056a 100644
--- a/tools/testing/selftests/bpf/prog_tests/task_pt_regs.c
+++ b/tools/testing/selftests/bpf/prog_tests/task_pt_regs.c
@@ -3,18 +3,22 @@
 #include <test_progs.h>
 #include "test_task_pt_regs.skel.h"
 
+/* uprobe attach point */
+static void trigger_func(void)
+{
+	asm volatile ("");
+}
+
 void test_task_pt_regs(void)
 {
 	struct test_task_pt_regs *skel;
 	struct bpf_link *uprobe_link;
-	size_t uprobe_offset;
-	ssize_t base_addr;
+	ssize_t uprobe_offset;
 	bool match;
 
-	base_addr = get_base_addr();
-	if (!ASSERT_GT(base_addr, 0, "get_base_addr"))
+	uprobe_offset = get_uprobe_offset(&trigger_func);
+	if (!ASSERT_GE(uprobe_offset, 0, "uprobe_offset"))
 		return;
-	uprobe_offset = get_uprobe_offset(&get_base_addr, base_addr);
 
 	skel = test_task_pt_regs__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "skel_open"))
@@ -32,7 +36,7 @@ void test_task_pt_regs(void)
 	skel->links.handle_uprobe = uprobe_link;
 
 	/* trigger & validate uprobe */
-	get_base_addr();
+	trigger_func();
 
 	if (!ASSERT_EQ(skel->bss->uprobe_res, 1, "check_uprobe_res"))
 		goto cleanup;